Acoustical Physics最新文献

The formulation of the problem of surface control of an electroactive unidirectional multicomponent elastic wave propagation in an infinite piezoelectric waveguide over a finite time interval is discussed. Based on the conditions for conjugation of electromechanical fields on the surface of piezoelectric media, as well as on the nature of possible surface electromechanical effects, a variety of surface dynamic effects is considered through the components of the elastic displacement vector, the mechanical stress tensor, the tangential component of the electric field strength and the normal component of the electric field displacement. The possibility of setting the control problem in the case of three-component electroacoustic waves depending on the anisotropy of the piezoelectric material of the waveguide is studied. The anisotropy of a piezoelectric medium leads to the formulation of an initial-boundary mathematical problem for controlling the motion of a multicomponent system. The variety of surface actions leads to the formulation of heterogeneous initial-boundary mathematical problems with surface actions of the first kind, with surface actions of the second kind, as well as for the case of mixed surface actions. An invariant record of heterogeneous initial-boundary mathematical problems is proposed in the form of a system of inhomogeneous quasi-static electro-elasticity equations, with homogeneous boundary conditions and inhomogeneous conditions of the initial and final states.

A 128°YX-LiNbO₃-based low-insertion-loss and high-frequency surface acoustic wave (SAW) filter was proposed using COMSOL Multiphysics. The spurious response was suppressed by changing the electrode thickness, reflector period, and reflector structure, after optimization. First, the thickness of the electrode was increased to concentrate the SAW energy on the surface of the piezoelectric material to reduce the propagation loss. Next, an interdigital transducer (IDT) reflector was designed to reduce the insertion loss caused by the spurious response and combined with the optimization of the reflector period. Finally, using this reflector structure when the thickness of the electrode was 0.4 μm, a SAW filter with a center frequency of 2520.5 MHz was designed. The results of the finite element method (FEM) revealed that the insertion loss at the center frequency was –0.1356 dB, the out-band suppression was greater than 30 dB, and the –3 dB bandwidth was greater than 97 MHz.

We consider the diffraction of a planar acoustic wave in a 2D sector with the central angle ({{2pi } mathord{left/ {vphantom {{2pi } n}} right. kern-0em} n}), (n in mathbb{N}). If (n) is even, then the solution of this problem is straightforward by the reflection method. For odd (n), we present an efficient algorithm to evaluate the time-domain solution of this problem. We use this solution with (n = 1) and (n = 3) to study the accuracy of the discontinuous Galerkin method applied to the acoustical system in a domain with corners.

The approach to identifying polycrystalline metal materials based on linear prediction analysis is introduce. The complex microstructure of polycrystalline metals results in different reflection, scattering and attenuation to ultrasonic waves. Based on the interaction between ultrasonic waves and microstructure of polycrystalline metals, this paper proposes a method to determine important items from tampering by using linear prediction coefficient (LPC). The linear prediction coefficient of the target item is extracted by the ultrasonic probe as its ultrasonic fingerprint signature. It is found that LPC ultrasonic fingerprint performs well as an authenticating technology to verify whether a specific item is genuine. This study provides a basis for the identification of polycrystalline metal materials with the same material and appearance.

A mode-matching analysis of infinite cylindrical duct with a partial absorbing internal surface is considered. The solution for the field terms are determined in form of eigenmodes which are matched across the boundary of each junction discontinuity. Numerical results are performed to show the influence of the different parameters such as waveguide radius, length of the lined part and acoustic absorbing lining on the propagation phenomenon. The method is also compared with the Wiener–Hopf technique which is more difficult to implement and very good corroboration is observed.

Eigenfrequencies and trapped modes are studied in an isotropic and homogeneous elastic half-strip. For different configurations of rigidly clamped and the traction-free zones, information was obtained about the absence or presence of eigenfrequencies below, and in some cases even above, the cutoff point of the continuous spectrum. Estimates of the multiplicity of the discrete spectrum are derived and various asymptotic representations of trapped modes and their frequencies are constructed.